1). Field of the Invention
Embodiments of the invention relate to the apparatus and method of using the apparatus for processing semiconductor substrates. In particular, the apparatus and method of using the apparatus for the deposition of an epitaxial semiconductor layer with reduced auto-doping and backside defects.
2). Background
FIG. 1A relates to an epitaxial processing apparatus 100 that may be used for epitaxial deposition. Substrate 102, which may be heated by upper heat lamps 106, is positioned over a susceptor 104, which may be heated by lower heat lamps 107. Upper dome 108 and lower dome 109, which may be quartz, enclose the processing chamber 113. Lift arms 101 and susceptor arms 105 move so as to separate from each other, thus separating the substrate 102 from the susceptor 104, and so as to position the processed substrate 102 to be removed from the processing chamber 113 by a robot (not shown) and replaced by an unprocessed substrate 102.
The epitaxial deposition of a low doped semiconductor layer on a highly doped substrate may often result in substantial auto-doping of the epitaxial low doped layer. Referring to FIG. 1B, during a high temperature epitaxial deposition process, dopant from the backside of the substrate 102 may diffuse out of the substrate 102 and into the wafer-susceptor gap 112. With a build-up of dopant in the wafer-susceptor gap 112, some dopant may migrate around the edge of the substrate 102 to the topside of the substrate 102, where the epitaxial layer is being formed. This phenomena is known as auto-doping 110 and results in the auto-dopants 110 mixing into the epitaxial layer being formed, particularly near the edge of the substrate 102. FIG. 1C demonstrates the auto-doping effect on resistivity 111. The extra auto-dopants 110 result in lowering the resistivity of the epitaxial layer near the edge, thus limiting the maximum resistivity of the epitaxial layer that may be formed on a highly doped substrate 102. This problem is particularly acute when boron is the dopant in a highly doped P+ substrate 102.
Oxidizing the backside of the substrate 102 may help seal the backside of the P+ substrate 102, thus reducing the out-diffusion of dopant into the wafer-susceptor gap 112. Backsealing may be effective, however this approach may be expensive because the oxide must be deposited and then removed, thus requiring at least two extra steps.
Another approach involves lowering the processing temperature during the epitaxial deposition process, thus substantially lowering the out-diffusion of dopant into the wafer-susceptor gap 112. Although this approach may be effective in reducing auto-doping, it also substantially reduces the rate of epitaxial growth on the substrate 102, thus substantially reducing throughput.
One approach involves adding more dopant to the middle of the wafer to provide a more uniform resistivity across the entire wafer. However, this process is only effective for the deposition of a low resistivity epitaxial layer. The process is limited to an epitaxial layer in the range of only about 1.5 to 3.0 ohms/sq.